Phosphor based light sources having a polymeric long pass reflector

ABSTRACT

A light source includes an LED that emits excitation light, a polymeric multilayer reflector that reflects the excitation light and transmits visible light, and a layer of phosphor material spaced apart from the LED. The phosphor material emits visible light when illuminated with the excitation light. The polymeric multilayer reflector reflects excitation light onto the phosphor material. The layer of phosphor material is disposed between the LED and the polymeric multilayer reflector.

CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application Nos.60/443,274, 60/443,232, and 60/443,235 all filed 27 Jan. 2003, and allincorporated by reference herein.

RELATED PATENT APPLICATIONS

The following co-owned and concurrently filed U.S. patent applicationsare incorporated herein by reference: “METHODS OF MAKING PHOSPHOR BASEDLIGHT SOURCES HAVING AN INTERFERENCE REFLECTOR”, application Ser. No.10/727,023; “PHOSPHOR BASED LIGHT SOURCE COMPONENT AND METHOD OFMAKING”, application Ser. No. 10/726,790; “PHOSPHOR BASED LIGHT SOURCEHAVING A FLEXIBLE SHORT PASS REFLECTOR”, application Ser. No.10/726,995; “PHOSPHOR BASED LIGHT SOURCES HAVING A NON-PLANAR LONG PASSREFLECTOR”, application Ser. No. 10/727,072; “PHOSPHOR BASED LIGHTSOURCES HAVING A NON-PLANAR LONG PASS REFLECTOR AND METHOD OF MAKING”,application Ser. No. 10/727,026; and “PHOSPHOR BASED LIGHT SOURCESHAVING A NON-PLANAR SHORT PASS REFLECTOR AND METHOD OF MAKING”,application Ser. No. 10/726,968.

FIELD OF THE INVENTION

The present invention relates to light sources. More particularly, thepresent invention relates to light sources in which light emitted from alight emitting diode (LED) impinges upon and excites a phosphormaterial, which in turn emits visible light.

DISCUSSION

White light sources that utilize LEDs in their construction can have twobasic configurations. In one, referred to herein as direct emissiveLEDs, white light is generated by direct emission of different coloredLEDs. Examples include a combination of a red LED, a green LED, and ablue LED, and a combination of a blue LED and a yellow LED. In the otherbasic configuration, referred to herein as LED-excited phosphor-basedlight sources (PLEDs), a single LED generates a beam in a narrow rangeof wavelengths, which beam impinges upon and excites a phosphor materialto produce visible light. The phosphor can comprise a mixture orcombination of distinct phosphor materials, and the light emitted by thephosphor can include a plurality of narrow emission lines distributedover the visible wavelength range such that the emitted light appearssubstantially white to the unaided human eye.

An example of a PLED is a blue LED illuminating a phosphor that convertsblue to both red and green wavelengths. A portion of the blue excitationlight is not absorbed by the phosphor, and the residual blue excitationlight is combined with the red and green light emitted by the phosphor.Another example of a PLED is an ultraviolet (UV) LED illuminating aphosphor that absorbs and converts UV light to red, green, and bluelight.

Advantages of white light PLEDs over direct emission white LEDs includebetter color stability as a function of device aging and temperature,and better batch-to-batch and device-to-device coloruniformity/repeatability. However, PLEDs can be less efficient thandirect emission LEDs, due in part to inefficiencies in the process oflight absorption and re-emission by the phosphor.

A white light PLED can comprise a UV emitting semiconductor die (chip)in a reflective heat sink. The reflective heat sink can also serve topartially collimate the UV light. The UV light illuminates the undersideof a phosphor-containing layer, which absorbs at least a portion of theUV light and emits light at multiple wavelengths in the visible regionto provide a source appearing substantially white to the ordinaryobserver. FIG. 1 shows one configuration of such a PLED 10. The PLEDincludes a semiconducting LED 12 mounted in a well of an electricallyconductive heat sink 14 that also reflects some of the light emittedfrom LED 12 toward a phosphor-reflector assembly 16. The assembly 16 canreside in an optically transparent potting material 18 which can beshaped to provide a lens feature 20 to tailor the light emitted by PLED10. The phosphor assembly 16 is shown in greater detail in FIG. 2. Thephosphor is formed into a layer 22 from a combination of one or morephosphor materials mixed with a binder. A long-pass (LP) reflector 24,that reflects the UV excitation light but transmits the visible emittedlight, can be applied to the top surface of phosphor layer 22. Ashort-pass (SP) reflector 26, that reflects visible light but transmitsUV light, can be applied to the bottom of layer 22.

The optimum thickness of the phosphor layer for a given phosphorconcentration is a compromise between efficiently absorbing the UV light(favoring an optically thick phosphor layer) and efficiently emittingvisible light (favoring an optically thin phosphor layer). Further,since the intensity of UV light is greatest at the bottom of phosphorlayer 22, and useful light is being extracted from the top of phosphorlayer 22, increasing the thickness of phosphor layer 22 above theoptimum thickness will rapidly reduce overall PLED output andefficiency.

The presence of LP reflector 24 and SP reflector 26 can enhance theefficiency of PLED 10. The LP reflector 24 reflects the UV light that isnot absorbed by phosphor layer 22, and that would otherwise be wasted,back onto the phosphor layer 22. This increases the effective pathlength of the UV light through the phosphor layer, increasing the amountof UV light absorbed by the phosphor for a given phosphor layerthickness. The optimum phosphor layer thickness can thus be reducedcompared to a construction without LP reflector 24, increasing theefficiency of light generation.

Another significant loss in the PLED is due to the directionallyuncontrolled generation of light in the phosphor layer, resulting inhalf of the visible light generated in phosphor layer 22 being directedback towards the LED. Some of this light can be captured by reflectionoff the sloped walls of the heat sink, but much of the light isscattered, absorbed, or reduced in quality. This loss can be reduced byplacing SP reflector 26 as shown between LED 12 and phosphor layer 22.

It would be advantageous to even further enhance the efficiency of PLEDconstructions. It would also be advantageous to simplify and reduce thecost of manufacture of PLEDs.

BRIEF SUMMARY

The present application discloses PLEDs that utilize polymer multilayeroptical films for the filtering components, i.e., the LP and SPreflectors. The multilayer optical films include individual opticallayers, at least some of which are birefringent, arranged into opticalrepeat units through the thickness of the film. Adjacent optical layershave refractive index relationships that maintain reflectivity and avoidleakage of p-polarized light at moderate to high incidence angles. TheSP reflector comprises optical repeat units having a thickness gradientthat produces a reflection band positioned to reflect visible lightemitted by the phosphor and transmit UV excitation light. The LPreflector comprises optical repeat units having a different thicknessgradient that produces a reflection band positioned to reflect the UVexcitation light and transmit the visible light emitted by the phosphor.As a component of the PLED, the polymer multilayer optical film(s) canhave a flat configuration or at least one can be embossed or otherwiseshaped to be curved, whether in the shape of a sphere, paraboloid,ellipsoid, or other shape.

Methods of manufacturing PLEDs are disclosed, which methods includeforming a sheet material that includes at least one polymer multilayeroptical film and a phosphor layer. In some cases the phosphor can besandwiched between two polymer multilayer optical films: one SPreflector, and one LP reflector. In other cases the phosphor layer canbe applied to only one polymer multilayer optical film. The polymermultilayer optical film(s) and phosphor layer form a phosphor-reflectorassembly. Individual pieces of the phosphor-reflector assembly can becut from the sheet material and subsequently immersed in a transparentpotting material or injection-molded to form a first optical componentwhich is then coupled to a separately manufactured LED component. Thesheet material can include a carrier film to hold and store thephosphor-reflector assembly pieces in a convenient roll form untilneeded. The PLED can be made by joining a lower portion comprising theLED to an upper portion comprising a phosphor-reflector assembly. Alsoin some cases the sheet material can be embossed

The present specification discloses PLED embodiments in which a curvedLP reflector is spaced apart from the phosphor layer, or at least from acentral bright portion thereof, so that any UV excitation light notabsorbed by the phosphor layer will impinge on the LP reflector over alimited range of incidence angles and be more efficiently reflected backonto the phosphor layer.

The present application discloses PLED embodiments that utilize an airgap proximate at least one of the multilayer optical films and thephosphor layer to promote total internal reflection.

The present application discloses PLED embodiments that utilizecombinations of non-imaging concentrator elements to enhance theperformance of the LP and/or SP reflector.

The present application also discloses PLED embodiments in which theLED, the LP reflector, and the phosphor layer are arranged such thatexcitation light from the LED is reflected directly onto a front majorsurface of the phosphor layer.

These and other aspects of disclosed embodiments will be apparent fromthe detailed description below. In no event, however, should the abovesummaries be construed as limitations on claimed subject matter, whichsubject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the specification, reference is made to the appendeddrawings, where like reference numerals designate like elements, andwherein:

FIG. 1 is a schematic sectional view of a LED-excited phosphor-basedlight source (PLED);

FIG. 2 is a sectional view of a phosphor-reflector assembly used in thesource of FIG. 1;

FIG. 3 depicts a roll comprising a phosphor-reflector assembly in sheetform and subdivided into individual pieces;

FIG. 4 is a schematic sectional view illustrating individual pieces ofthe phosphor-reflector assembly on a carrier film;

FIGS. 5-7 are schematic sectional views of alternative PLEDconstructions;

FIG. 8 depicts a portion of still another PLED construction;

FIG. 9 is a schematic sectional view of still another PLED construction;

FIG. 10 is a schematic side view of another PLED construction thatutilizes front surface illumination, as does the embodiment of FIG. 9;

FIG. 11 is a schematic side view of a PLED construction that makes useof an arrangement of nonimaging concentrators; and

FIG. 12 is a close-up view of a portion of FIG. 11.

FIGS. 13-14 are sectional views of other embodiments of aphosphor-reflector assembly used in the source of FIG. 1;

FIG. 15 is a schematic sectional view of a phosphor based light sourcetwo part component system;

FIG. 16 is a graph of a light intensity spectrum of Examples 1 and 2;

FIG. 17 is a graph of a light intensity spectrum of Examples 3, 4, and5;

FIG. 18 is a graph of a light intensity spectrum of Examples 6, 7, and8; and

FIG. 19 is a graph of a light intensity spectrum of Examples 9 and 10.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

While the use of one or both of LP reflector 24 and SP reflector 26 asshown in FIGS. 1-2 can improve system efficiency, the improvement islimited due to certain reflectors' poor spectral selectivity and poorreflectivity at oblique angles of incidence. LP mirrors or filters basedon scattering processes can achieve relatively constant performance as afunction of incidence angle, but have poor spectral selectivity. LP andSP mirrors constructed from an inorganic dielectric material stack canhave good spectral selectivity over a narrow range of incidence angles,but suffer from spectral blue-shifts with increasing incidence angle andlow reflectivity (high transmission) of p-polarized light at moderate tohigh incidence angles. Since phosphor particles scatter the UVexcitation light, and emit their own light over a wide range of angles,conventional LP and SP mirrors are not highly effective in managinglight within the phosphor-reflector assembly.

The performance of PLEDs can be increased by using polymeric multilayeroptical films, i.e., films having tens, hundreds, or thousands ofalternating layers of at least a first and second polymer material,whose thicknesses and refractive indices are selected to achieve adesired reflectivity in a desired portion of the spectrum, such as areflection band limited to UV wavelengths or a reflection band limitedto visible wavelengths. See, for example, U.S. Pat. No. 5,882,774 (Jonzaet al.). Although reflection bands produced by these films alsoexperience a blue-shift with incidence angle similar to the blue-shiftassociated with stacks of inorganic isotropic materials, the polymericmultilayer optical films can be processed so that adjacent layer pairshave matching or near-matching, or deliberately mismatched refractiveindices associated with a z-axis normal to the film such that thereflectivity of each interface between adjacent layers, for p-polarizedlight, decreases slowly with angle of incidence, is substantiallyindependent of angle of incidence, or increases with angle of incidenceaway from the normal. Hence, such polymeric multilayer optical films canmaintain high reflectivity levels for p-polarized light even at highlyoblique incidence angles, reducing the amount of p-polarized lighttransmitted by the reflective films compared to conventional inorganicisotropic stack reflectors. In order to achieve these properties, thepolymer materials and processing conditions are selected so that, foreach pair of adjacent optical layers, the difference in refractive indexalong the z-axis (parallel to the thickness of the film) is no more thana fraction of the refractive index difference along the x- or y-(in-plane) axes, the fraction being 0.5, 0.25, or even 0.1.Alternatively, the refractive index difference along the z-axis can beopposite in sign to the in-plane refractive index differences.

The use of polymeric multilayer optical films also makes available avariety of new PLED embodiments and methods of construction due to theflexibility and formability of such films, whether or not they also havethe refractive index relationships referred to above. For example,polymeric multilayer optical film can be permanently deformed byembossing, thermoforming, or other known means to have a 3-dimensionalshape such as a portion of a paraboloid, a sphere, or an ellipsoid. Seegenerally published application U.S. 2002/0154406 (Merrill et al.). Seealso U.S. Pat. No. 5,540,978 (Schrenk) for additional polymericmultilayer film embodiments. Unlike conventional inorganic isotropicstacks, which are normally vapor deposited layer-by-layer onto a rigid,brittle substrate, polymeric multilayer optical films can be made inhigh volume roll form, and can also be laminated to other films andcoated, and can be die cut or otherwise subdivided into small pieces foreasy inCompany into an optical system such as a PLED as furtherexplained below. Suitable methods of subdividing polymeric multilayeroptical film are disclosed in pending U.S. application Ser. No.10/268,118, filed Oct. 10, 2002.

A wide variety of polymer materials are suitable for use in multilayeroptical films for PLEDs. However, particularly where the PLED comprisesa white-light phosphor emitter coupled with a UV LED excitation source,the multilayer optical film preferably comprises alternating polymerlayers composed of materials that resist degradation when exposed to UVlight. In this regard, a particularly preferred polymer pair ispolyethylene terephthalate (PET)/co-polymethylmethacrylate (co-PMMA).The UV stability of polymeric reflectors can also be increased by theinCompany of non-UV absorbing light stabilizers such as hindered aminelight stabilizers (HALS). In some cases the polymeric multilayer opticalfilm can also include transparent metal or metal oxide layers. See e.g.PCT Publication WO 97/01778 (Ouderkirk et al.). In applications that useparticularly high intensity UV light that would unacceptably degradeeven robust polymer material combinations, it may be beneficial to useinorganic materials to form the multilayer stack. The inorganic materiallayers can be isotropic, or can be made to exhibit form birefringence asdescribed in PCT Publication WO 01/75490 (Weber) and thus have thebeneficial refractive index relationships that yield enhancedp-polarization reflectivity as described above. However, in most casesit is most convenient and cost effective for the multilayer optical filmto be substantially completely polymeric, free of inorganic materials.

FIG. 3 depicts a roll of sheet material 30, which material comprises atleast one polymeric multilayer optical film and a substantially uniformphosphor layer applied to the multilayer optical film by a coatingoperation. The sheet material can also comprise a second polymericmultilayer optical film applied in such a way that the phosphor layer issandwiched between the first and second polymeric multilayer opticalfilm, as seen in FIG. 2. Additional layers and coatings providingdesired mechanical, chemical, and/or optical properties can also beincluded. See U.S. Pat. No. 6,368,699 (Gilbert et al.). The sheetmaterial 30 also preferably includes a carrier film. The sheet materialis kiss-cut by mechanical means such as a knife, precision die cutting,or by scanning laser radiation as described in the pending '118application referred to above. The kiss-cut lines define discrete pieces32 of the sheet material, but exclusive of the carrier film whichremains intact. The pieces 32 can have a cross-sectional constructionsimilar to that shown in FIG. 2, and can be of arbitrarily small size.They are conveniently carried by the underlying carrier film 34 as shownin FIG. 4. During production of the PLEDs—and independent of theconstruction of the LED source—pieces 32 can be removed from the carrierfilm and placed in individual molds to which potting material is, or waspreviously, added, thus forming PLEDs as depicted in FIG. 1 but whereinthe reflector components use polymeric multilayer optical films.

FIGS. 5-7 depict alternative constructions of PLEDs utilizing aconcave-shaped multilayer optical film LP reflector. Spacing the LPreflector away from the phosphor and curving it in towards the phosphorand towards the LED 12 helps reduce the range of incidence angles ofexcitation light impinging on the LP reflector, thereby reducing theleakage of UV light through the LP reflector caused by the blue-shifteffect discussed above. Preferably the multilayer optical film ispermanently deformed by embossing or other suitable process into aconcave surface of suitable shape before immersion in transparent medium18. The multilayer optical films, whether LP or SP, are specularreflectors within their respective reflection bands. Diffuse reflectionfrom a multilayer optical film is typically negligible.

In FIG. 5, PLED 40 includes a relatively small area phosphor layer 42disposed on an optional SP reflector 44 composed of a polymericmultilayer optical film. LP reflector 46 has been embossed to acquire aconcave shape and positioned next to the other components (42, 44) ofthe phosphor-reflector assembly. LED 12 and heat sink 14 are arranged todirect UV excitation light emitted by the LED toward the central portionof phosphor layer 42. Preferably, the UV light has its highest fluenceat or near the center of phosphor layer 42. UV light not absorbed in itsinitial traversal of phosphor layer 42 passes through a region 48between LP reflector 46 and phosphor layer 42 before being reflected byLP reflector 46 back towards the phosphor layer. The region 48 can becomposed of transparent potting material 18, or alternatively of anotherpolymeric material, or air (or other gas), or glass. LP reflector 46 ispreferably shaped to maximize the amount of UV excitation lightreflected back to the phosphor.

FIG. 6 shows a PLED 50 similar to PLED 40, except that the size of thephosphor layer 52, SP reflector 54, and LP reflector 56 are increased.For a given distance from LED 12 to the phosphor layer, and the sameheat sink 14 geometry, the larger LP reflector 56 will yield a higherconcentration of light in the center of the phosphor layer. The smaller,central emitting area of the phosphor layer presents a smaller range ofincidence angles of phosphor-emitted light to the surface of the LPreflector, improving overall PLED efficiency. As before, region 58 canbe composed of potting material 18 or another polymeric material, or air(or other gas), or glass.

PLED 60, shown in FIG. 7, is similar to PLED 50, except the LP reflector66 now forms an outer surface of the light source. Region 68 can befilled with potting material 18 or other transparent medium.

The phosphor layers of FIGS. 5-7 can be continuous, or patterned tolimit the phosphor to where it is most effective. Moreover, in theembodiments of FIGS. 1 and 5-7 and other embodiments where thephosphor-reflector assembly is disposed above and spaced apart from theLED, the PLED can be manufactured in two halves: one containing the LEDwith heat sink, and the other containing the phosphor layer andmultilayer reflector(s). The two halves can be made separately, and thenbe joined or otherwise secured together. This construction technique canhelp simplify manufacturing and increase overall yields.

FIG. 8 demonstrates a concept that can be applied beneficially to theother embodiments herein: providing an air gap between the LED and thephosphor layer, and/or providing an air gap proximate to one or moreelements of the phosphor-reflector assembly. Only some elements of aPLED are shown in the figure for simplicity of description. An air gap70 is shown between LED 12 and phosphor layer 72, adjacent multilayeroptical film SP reflector 74. The air gap has a minimal detrimentaleffect on UV light from the LED reaching the phosphor layer because ofthe relatively small angles involved. But the air gap enables totalinternal reflection (TIR) of light traveling at high incidence angles,such as light traveling in the SP reflector, the phosphor layer, and theLP reflector. In the embodiment of FIG. 8 the efficiency of the SPreflector is enhanced by allowing TIR at the lower surface of reflector74. Alternatively, SP reflector 74 can be eliminated and the air gap canbe formed directly under phosphor layer 72. An air gap can also beformed at the upper side of phosphor layer 72, or adjacent to the LPreflector at its upper or lower surface. One approach for providing theair gap involves the use of known microstructured films. Such films havea substantially flat surface opposed to a microstructured surface. Themicrostructured surface can be characterized by a single set of linearv-shaped grooves or prisms, multiple intersecting sets of v-shapedgrooves that define arrays of tiny pyramids, one or more sets of narrowridges, and so forth. When the microstructured surface of such a film isplaced against another flat film, air gaps are formed between theuppermost portions of the microstructured surface.

As phosphors convert light of one wavelength (the excitation wavelength)to other wavelengths (the emitted wavelengths), heat is produced. Thepresence of an air gap near the phosphor may significantly reduce heattransmission from the phosphor to surrounding materials. The reducedheat transfer can be compensated for in other ways, such as by providinga layer of glass or transparent ceramic near the phosphor layer that canremove heat laterally.

Still another approach of improving the efficiency of PLEDs is toconfigure the LED, phosphor layer, arid LP reflector, such that at leastsome of the UV light from the LED is reflected by the LP reflectordirectly onto the top (viewing) surface of the phosphor layer, ratherthan directing all of the UV light onto the bottom surface of thephosphor layer. FIG. 9 shows such a PLED 80. The heat sink 14′ has beenmodified from above embodiments so that the LED 12 and the phosphorlayer 82 can be mounted generally co-planar. An SP reflector 84 is shownunderneath the phosphor layer, but in many eases will not be required.This is because LP reflector 86, which has been embossed in the form ofa concave ellipsoid or similar shape, directs UV excitation lightdirectly from the LED onto the upper surface of phosphor layer 82, whichsurface faces the front of PLED 80. The LED and phosphor layer arepreferably disposed at the foci of the ellipsoid. The visible lightemitted by the phosphor layer is transmitted by LP reflector 86 andcollected by the rounded front end of the PLED body to form the desiredpattern or visible (preferably white) light.

Directing excitation light directly at the front surface of the phosphorlayer has a number of benefits. The brightest portion of the phosphorlayer—where the excitation light is the strongest—now is exposed at thefront of the device rather than being obscured through the thickness ofthe phosphor layer. The phosphor layer can be made substantially thickerso that it absorbs substantially all of the UV excitation light, withoutconcern for the thickness/brightness tradeoff referred to above. Thephosphor can be mounted on a broadband metal mirror, including silver orenhanced aluminum.

FIG. 10 shows schematically another PLED embodiment where the LED lightimpinges on the front surface of the phosphor layer, but wherein some ofthe LED light also impinges on the back surface. In this embodiment,some light emitted by LED 12 impinges on the back surface of phosphorlayer 92, but some LED light also reflects off of the concave-shaped LPreflector 96 to strike the front surface of phosphor layer 92 withouttraversing through the phosphor. Visible light emitted by phosphor layer92 then passes through the LP reflector 96 towards the viewer or objectto be illuminated. The LED, phosphor layer, and LP reflector can all beimmersed or attached to a transparent potting medium as shown inprevious embodiments.

FIG. 11 shows schematically another PLED embodiment, whereincombinations of non-imaging concentrators are arranged to enhance theoperation of the multilayer optical films. Specifically, concentratorelements 100 a, 100 b, 100 c are provided as shown between the LED 12,SP reflector 104, phosphor layer 102, and LP reflector 106. Theconcentrator elements have the effect of reducing the angular spread oflight impinging on the multilayer reflectors, thus reducing theblue-shift of the reflection band discussed above in connection withFIGS. 5-7. The concentrator elements may be in the form of simpleconical sections with flat sidewalls, or the sidewalls can take on amore complex curved shape as is known to enhance collimation or focusingaction depending on the direction of travel of the light. In any eventthe sidewalls of the concentrator elements are reflective and the twoends (one small, one large) are not. In FIG. 11, LED 12 is disposed atthe small end of concentrator 100 a. Concentrator element 100 a collectsa wide angular range of light emitted by the LED, which range is reducedby the time such light has traveled to the large end of concentratorelement 100 a, where SP reflector 104 is mounted. The SP reflectortransmits the UV excitation light to concentrator element 100 b, whichconcentrates such light onto phosphor layer 102 (while increasing theangular spread of the light). Wide angular range visible light emitteddownwardly by phosphor layer 102 is converted by concentrator element100 b to a more narrow angular range at SP reflector 104, where it isreflected back up towards the phosphor layer 102. Meanwhile, UV lightthat leaks through phosphor layer 102 and visible light emitted upwardlyby phosphor layer 102 initially has a wide angular spread, but isconverted by concentrator element 100 c to a smaller angular spread sothat LP reflector 106 will better transmit the visible light emitted bythe phosphor and reflect the UV light back towards the phosphor layer.

To capture as much LED excitation light as possible, the small end ofconcentrator element 100 a can have a cavity so as to capture at leastsome light emitted by the sides of the LED, as shown in FIG. 12.

The embodiments disclosed herein are operative with a variety ofphosphor materials. The phosphor materials are typically inorganic incomposition, having excitation wavelengths in the 300-450 nanometerrange and emission wavelengths in the visible wavelength range. In thecase of phosphor materials having a narrow emission wavelength range, amixture of phosphor materials can be formulated to achieve the desiredcolor balance, as perceived by the viewer, for example a mixture ofred-, green- and blue-emitting phosphors. Phosphor materials havingbroader emission bands are useful for phosphor mixtures having highercolor rendition indices. Desirably, phosphors should have fast radiativedecay rates. A phosphor blend can comprise phosphor particles in the1-25 micron size range dispersed in a binder such as epoxy, adhesive, ora polymeric matrix, which can then be applied to a substrate, such as anLED or a film. Phosphors that convert light in the range of about 300 to470 nm to longer wavelengths are well known in the art. See, forexample, the line of phosphors offered by Phosphor Technology Ltd.,Essex, England. Phosphors include rare-earth doped garnets, silicates,and other ceramics. The term “phosphor” as used herein can also includeorganic fluorescent materials, including fluorescent dyes and pigments.Materials with high stability under 300-470 nm radiation are preferred,particularly inorganic phosphors.

Glossary of Certain Terms

-   LED: a diode that emits light, whether visible, ultraviolet, or    infrared, and whether coherent or incoherent. The term as used    herein includes incoherent (and usually inexpensive) epoxy-encased    semiconductor devices marketed as “LEDs”, whether of the    conventional or super-radiant variety. The term as used herein also    includes semiconductor laser diodes.-   Visible Light: light that is perceptible to the unaided human eye,    generally in the wavelength range from about 400 to 700 nm.-   Optical Repeat Unit (“ORU”): a stack of at least two individual    layers which repeats across the thickness of a multilayer optical    film, though corresponding repeating layers need not have the same    thickness.-   Optical thickness: the physical thickness of a given body times its    refractive index. In general, this is a function of wavelength and    polarization.-   Reflection band: a spectral region of relatively high reflectance    bounded on either side by regions of relatively low reflectance.-   Ultraviolet (UV): light whose wavelength is in the range from about    300 to about 400 nm.-   White light: light that stimulates the red, green, and blue sensors    in the human eye to yield an appearance that an ordinary observer    would consider “white”. Such light may be biased to the red    (commonly referred to as warm white light) or to the blue (commonly    referred to as cool white light). Such light can have a color    rendition index of up to 100.    Further Discussion

The interference reflector described herein includes reflectors that areformed of organic, inorganic or a combination of organic and inorganicmaterials. The interference reflector can be a multilayer interferencereflector. The interference reflector can be a flexible interferencereflector. A flexible interference reflector can be formed frompolymeric, non-polymeric materials, or polymeric and non-polymericmaterials. Exemplary films including a polymeric and non-polymericmaterial are disclosed in U.S. Pat. Nos. 6,010,751 and 6,172,810 and EP733,919A2, all incorporated by reference herein.

The interference reflector described herein can be formed from flexible,plastic, or deformable materials and can itself be flexible, plastic ordeformable. These interference reflectors can be deflectable or curvedto a radius usable with conventional LEDs, i.e., from 0.5 to 5 mm. Theseflexible interference reflectors can be deflected or curved and stillretain its pre-deflection optical properties.

Known self-assembled periodic structures, such as cholesteric reflectingpolarizers and certain block copolymers, are considered to be multilayerinterference reflectors for purposes of this application. Cholestericmirrors can be made using a combination of left and right handed chiralpitch elements.

In an illustrative embodiment, a long-pass filter that partiallytransmits all wavelengths of blue light can be used in combination witha thin yellow phosphor layer in order to direct some blue light from theLED back onto the phosphor layer after the first pass through thephosphor.

In addition to providing reflection of UV light, a function of themultilayer optical film can be to block transmission of UV light so asto prevent degradation of subsequent elements inside or outside the LEDpackage, including prevention of human eye damage. In some embodiments,it may be advantageous to incorporate a UV absorber on the side of theUV reflector furthest away from the LED. This UV absorber can be in, on,or adjacent to the multilayer optical film.

Although a variety of methods are known in the art for producinginterference filters, an all polymer construction can offer severalmanufacturing and cost benefits. If high temperature polymers with highoptical transmission and large index differentials are utilized in theof an interference filter, then an environmentally stable filter that isboth thin and very flexible can be manufactured to meet the opticalneeds of short-pass (SP) and (LP) filters. In particular, coextrudedmultilayer interference filters as taught in U.S. Pat. No. 6,531,230(Weber et al.) can provide precise wavelength selection as well as largearea, cost effective manufacturing. The use of polymer pairs having highindex differentials allows the construction of very thin, highlyreflective mirrors that are freestanding, i.e. have no substrate but arestill easily processed. Such interference structures will not crack orshatter or otherwise degrade either when thermoformed or when flexed toa radius of curvature as small as 1 mm.

An all polymeric filter can be thermoformed into various 3D shapes suchas e.g. hemispherical domes (as described below). However, care must betaken to control the thinning to the correct amount over the entiresurface of the dome to create the desired angular performance. Filtershaving a simple two dimensional curvature are easier to create than 3D,compound shaped filters. In particular, any thin and flexible filter canbe bent into a 2D shaped such as e.g. a part of a cylinder, in this casean all polymeric filter is not needed. Multilayer inorganic filters onthin polymeric substrates can be shaped in this manner, as well as caninorganic multilayers on glass substrates that are less than 200 micronsin thickness. The latter may have to be heated to temperatures near theglass transition point to obtain a permanent shape with low stress.

Optimum bandedges for long and short pass filters will depend on theemission spectra of both the LED and the phosphor in the system thefilters are designed to operate in. In an illustrative embodiment, for ashort pass filter, substantially all of the LED emission passes throughthe filter to excite the phosphor, and substantially all of the phosphoremissions are reflected by the filter so they do not enter the LED orits base structure where they could be absorbed. For this reason, theshort pass defining bandedge is placed in a region between the averageemission wavelength of the LED and the average emission wavelength ofthe phosphor. In an illustrative embodiment, the filter is placedbetween the LED and the phosphor. If however, the filter is planar, theemissions from a typical LED will strike the filter at a variety ofangles, and at some angle of incidence be reflected by the filter andfail to reach the phosphor. Unless the filter is curved to maintain anearly constant angle of incidence, one may desire to place the designbandedge at a wavelength larger than the midpoint of the phosphor andLED emission curves to optimize the overall system performance. Inparticular, very little of the phosphor emission is directed to thefilter near zero degrees angle of incidence because the included solidangle is very small.

In another illustrative embodiment, long pass reflective filters areplaced opposite the phosphor layer from the LED in order to recycle theLED excitation light back to the phosphor in order to improve systemefficiency. In the illustrative embodiment, a long pass filter may beomitted if the LED emissions are in the visible spectrum and largeamounts are needed to balance the phosphor color output. However, a longpass filter that partially transmits the shortwave light, such as e.g.blue light, can be used to optimize the angular performance of ablue-LED/yellow-phosphor system via the spectral angle shift that wouldpass more blue light at higher angles than at normal incidence.

In a further illustrative embodiment, the LP filter is curved, in orderto maintain a nearly constant angle of incidence of the LED emittedlight on the filter. In this embodiment, the phosphor and the LED bothface one side of the LP filter. At high angles of incidence, the LPfilter will not reflect the shortwave light. For this reason, the longwave bandedge of the LP filter can be placed at as long a wavelength aspossible while blocking as little of the phosphor emission as possible.Again, the bandedge placement can be changed to optimize the overallsystem efficiency.

The term “adjacent” is defined herein to denote a relative positioningof two articles that are near one another. Adjacent items can betouching, or spaced away from each other with one or more materialsdisposed between the adjacent items.

LED excitation light can be any light that an LED source can emit. LEDexcitation light can be UV, or blue light. Blue light also includesviolet and indigo light. LEDs include spontaneous emission devices aswell as devices using stimulated or super radiant emission includinglaser diodes and vertical cavity surface emitting laser diodes.

Layers of phosphor described herein can be a continuous or discontinuouslayer. The layers of phosphor material can be a uniform or non-uniformpattern. The layer of phosphor material can be plurality of regionshaving a small area such as, for example, a plurality of “dots” eachhaving an area in plan view of less than 10000 micrometers² or from 500to 10000 micrometers². In an illustrative embodiment, the plurality ofdots can each be formed from a phosphor which emits visible light at oneor more different wavelengths such as, for example, a dot emitting red,a dot emitting blue, and a dot emitting green. The dots emitting visiblelight at a plurality of wavelengths can be arranged and configured inany uniform or non-uniform manner as desired. For example, the layer ofphosphor material can be a plurality of dots with a non-uniform densitygradient along a surface or an area. The “dots” can have any regular orirregular shape, and need not be round in plan view. Phosphor materialcan be in a co-extruded skin layer of the multilayer optical film.

Structured phosphor layers can be configured in several ways to providebenefits in performance, as described below. When multiple phosphortypes are used to provide broader or fuller spectral output, light fromshorter wavelength phosphors can be re-absorbed by other phosphors.Patterns comprising isolated dots, lines, or isolated regions of eachphosphor type reduce the amount of re-absorption. This would beparticularly effective in cavity type constructions where unabsorbedpump light is reflected back to the phosphor pattern.

Multilayer structures can also reduce absorption. For example, it couldbe advantageous to form layers of each phosphor in sequence, with thelongest wavelength emitter nearest the excitation source. Light emittednearer the emitter will on average, undergo multiple scattering withinthe total phosphor layer to a greater extent than light emitted near theoutput surface. Since the shortest wavelength emitted is most prone tore-absorption, it is advantageous to locate the shortest wavelengthphosphor nearest to the output surface. In addition, it may beadvantageous to use different thicknesses for each layer, so as tocompensate for the progressively lower intensity of the excitation lightas it propagates through the multilayer structure. For phosphor layerswith similar absorption and emission efficiency, progressively thinnerlayers from excitation to output side would provide compensation for thedecreasing excitation intensity in each layer. It would also beadvantageous to place short pass filters in-between the differentphosphor layers so as to reduce emitted phosphor light from scatteringbackward and being re-absorbed by phosphor layers earlier in thesequence.

Forming film structures with phosphor coating also enables manufacturingof arrays of small structures suitable for dicing into individual unitsfor diodes. For example, an array of small domes or hemispheres could beprinted, each of which would be useful for reducing the “halo effect”sometimes present for PLED's (as described below).

Non-scattering phosphor layers can provide enhanced light output incombination with multilayer optical films. Non-scattering phosphorlayers can comprise conventional phosphors in an index-matched binder(for example, a binder with high index inert nanoparticles), nanosizeparticles of conventional phosphor compositions (for examples, whereparticle sizes are small and negligibly scatter light), or through theuse of quantum dot phosphors. Quantum dot phosphors are light emittersbased on semiconductors such as cadmium sulfide, wherein the particlesare sufficiently small so that the electronic structure is influencedand controlled by the particle size. Hence, the absorption and emissionspectra are controlled via the particle size. Quantum dots are disclosedin U.S. Pat. No. 6,501,091, incorporated by reference herein.

Embodiments are disclosed herein where a first optical componentcomprising a phosphor/reflector assembly can be later attached to an LEDbase; a heat sink can optionally include a transparent heat sink towhich the phosphor layer and interference filter may be attached. Thetransparent heat sink can be a layer of sapphire disposed between thephosphor layer/interference filter and the LED base. Most glasses have ahigher thermal conductivity than polymers and can be useful in thisfunction as well. Many other crystalline material's thermalconductivities are higher than most glasses and can be used here also.The sapphire layer can be contacted at the edges by a metal heat sink.

In an illustrative embodiment, prior to coating the interference filter(i.e., polymeric interference filter with a phosphor layer, the surfaceof the filter can be treated to promote adhesion of the coating. Theoptimum treatment depends both on the surface layer of the filter and onthe materials in the phosphor coating, specifically the binder used tohold the phosphor particles on the surface. The surface treatment can bea standard corona discharge treatment, or a corona discharge followed bya priming layer. The priming layer is typically less than 1 micronthick. Useful priming materials are PVDC, sulphonated polyesters andother amorphous polyesters such as Vitel, maleated copolymers such asBynel (Dupont) and Admer (Mitsui Chemicals), and EVA such as Elvax(Dupont). Binders for the phosphor layer can be a thermoplastic and/orthermoformable and can be a fluoropolymer, or silicon based material,for example.

Alternative priming layers include, for example, vacuum coated layers,preferably from energetic sources such as ion-beam or gas plasma sourceswherein the ions or plasma components bombard the polymer surface whiledepositing the priming layer. Such priming layers are typicallyinorganic material layers such as titania or silica layers.

Although much attention has been given to the use of phosphors fordown-converting short wavelength light to visible light, it is alsopossible to up-convert infrared radiation to visible light.Up-converting phosphors are well known in the art and typically use twoor more infrared photons to generate 1 visible photon. Infrared LEDsneeded to pump such phosphors have also been demonstrated and are veryefficient. Visible light sources that use this process can be made moreefficient with the addition of long-pass (LP) and short-pass (SP)filters although the functions of each are reversed in this casecompared to the down-converting phosphor systems. A SP filter can beused to direct IR light towards the phosphor while transmitting thevisible light, and an LP filter can be placed between the phosphor andLED to direct the emitted visible light outward towards the intendedsystem or user.

The lifetime of an SP or LP filter is preferably greater than or equalto the lifetime of the LED in the same system. The degradation of apolymeric interference filter can be due to overheating which can causematerial creep which changes the layer thickness values and thereforethe wavelengths that the filter reflects. In the worst case, overheatingcan cause the polymer materials to melt, resulting in rapid flow ofmaterial and change in wavelength selection as well as inducingnon-uniformities in the filter.

Degradation of polymer materials can also be induced by short wavelength(actinic) radiation such as blue, violet or UV radiation, depending onthe polymer material. The rate of degradation is dependent both on theactinic light flux and on the temperature of the polymer. Both thetemperature and the flux will in general, decrease with increasingdistance from the LED. Thus it is advantageous in cases of highbrightness LEDs, particularly UV LEDs, to place a polymeric filter asfar from the LED as the design can allow. Placement of the polymerfilter on a transparent heat sink as described above can also improvethe lifetime of the filter. For domed filters, the flux of actinicradiation decreases as the square of the distance from the LED. Forexample, a hemispherical MOF reflector with a 1 cm radius, placed with aunidirectional 1 watt LED at the center of curvature, would experiencean average intensity of 1/(2π) Watts/cm² (surface area of the dome=2πcm²). At a 0.5 cm radius, the average intensity on the dome would befour times of that value, or 2/π W/cm². The system of LED, phosphor, andmultilayer optical film can be designed with light flux and temperaturecontrol taken into consideration.

A reflective polarizer can be disposed adjacent the multilayer reflectorand/or adjacent the phosphor material. The reflective polarizer allowslight of a preferred polarization to be emitted, while reflecting theother polarization. The phosphor layer and other film components knownin the art can depolarize the polarized light reflected by reflectivepolarizer, and either by the reflection of the phosphor layer, orphosphor layer in combination with the multilayer reflector, light canbe recycled and increase the polarized light brightness of the solidstate light device (LED). Suitable reflective polarizers include, forexample, cholesteric reflective polarizers, cholesteric reflectivepolarizers with a ¼ wave retarder, DBEF reflective polarizer availablefrom 3M Company or DRPF reflective polarizer also available from 3MCompany. The reflective polarizer preferably polarizes light over asubstantial range of wavelengths and angles emitted by the phosphor, andin the case where the LED emits blue light, may reflect the LED emissionwavelength range as well.

Suitable multilayer reflector films are birefringent multilayer opticalfilms in which the refractive indices in the thickness direction of twoadjacent layers are substantially matched and have a Brewster angle (theangle at which reflectance of p-polarized light goes to zero) which isvery large or is nonexistant. This allows for the construction ofmultilayer mirrors and polarizers whose reflectivity for p-polarizedlight decreases slowly with angle of incidence, are independent of angleof incidence, or increase with angle of incidence away from the normal.As a result, multilayer films having high reflectivity (for both planesof polarization for any incident direction in the case of mirrors, andfor the selected direction in the case of polarizers) over a widebandwidth, can be achieved. These polymeric multilayer reflectorsinclude alternating layers of a first and second thermoplastic polymer.The alternating layers defining a local coordinate system with mutuallyorthogonal x- and y-axes extending parallel to the layers and with az-axis orthogonal to the x- and y-axes, and wherein at least some of thelayers are birefringent. The absolute value of the difference in indicesof refraction between the first and second layers is Δx, Δy, and Δzrespectively, for light polarized along first, second, and thirdmutually orthogonal axes. The third axis is orthogonal to the plane ofthe film where Δx is greater than about 0.05, and where Δz is less thanabout 0.05. These films are described, for example, in U.S. Pat. No.5,882,774, which is incorporated by reference herein.

FIG. 13 is a sectional view of another embodiment of aphosphor-reflector assembly 116 used, for example, in the source ofFIG. 1. A multilayer reflector 126 is shown adjacent a layer of phosphormaterial 122, however the multilayer reflector 126 need only bepositioned such that light can travel between the layer of phosphormaterial 122 and the multilayer reflector 126. The multilayer reflector126 reflects at least a portion of visible light and transmits LEDexcitation light such as, for example UV, or blue light. This multilayerreflector 126 can be referred to as a short-pass (SP) reflector, asdescribed above.

The multilayer reflector 126 can be positioned to receive light from anLED 12, as discussed herein. The multilayer reflector 126 can be anyuseable thickness. The multilayer reflector 126 can be 5 to 200micrometers thick or 10 to 100 micrometers thick. The multilayerreflector 126 can optionally be substantially free of inorganicmaterials.

The multilayer reflector 126 can be formed of a material that resistsdegradation when exposed to UV, blue, or violet light, such as discussedherein. The multilayer reflectors discussed herein can be stable underhigh intensity illumination for extended periods of time. High intensityillumination can be generally defined as a flux level from 1 to 100Watt/cm². Operating temperatures at the interference reflectors can be100° C. or less, or 65° or less. Suitable illustrative polymericmaterials can include UV resistant material formed from, for example,acrylic material, PET material, PMMA material, polystyrene material,polycarbonate material, THV material available from 3M (St. Paul,Minn.), and combinations thereof. These materials and PEN material canbe used for blue excitation light.

The multilayer reflector 126 can be positioned in any usableconfiguration with the LED 12, as described herein. In an illustrativeembodiment, the multilayer reflector 126 is positioned between the layerof phosphor 122 and the LED 12. In another illustrative embodiment, thelayer of phosphor 122 is positioned between the multilayer reflector 126and the LED 12. The multilayer reflector 126 can be configured totransmit UV or blue light and reflect at least a portion of the visiblelight spectrum such as green, yellow, or red light. In anotherillustrative embodiment, the multilayer reflector 126 can be configuredto transmit UV, blue or green light and reflect at least a portion ofthe visible light spectrum such as yellow or red light.

The layer of phosphor material 122 is capable of emitting visible lightwhen illuminated with excitation light emitted from an LED 12. The layerof phosphor material 122 can be any useable thickness. The layer ofphosphor material 122 can include any number of binders such as, forexample, a polyester material. In another illustrative embodiment thelayer of phosphor material 122 can include an adhesive material. In afurther illustrative embodiment, an adhesive material can be disposedbetween the layer of phosphor material 122 and the polymeric multilayerreflector 126. The adhesive material can be an optically functionaladhesive, i.e., it can include additional optical materials such as, forexample, dyes, or scattering particles.

The phosphor-reflector assembly 116 can be formed in a variety of ways.For example, the layer of phosphor material 122 can be disposed orcoated on the polymeric multilayer reflector 126. The layer of phosphormaterial 122 can be applied as a flowable material onto the polymericmultilayer reflector 126. The layer of phosphor material 122 can belaminated, as a solid layer, adjacent the polymeric multilayer reflector126. In addition, the layer of phosphor material 122 and the polymericmultilayer reflector 126 can be thermoformed sequentially orsimultaneously. The layer of phosphor can be compressible, elastomeric,and can even be contained in a foamed structure.

The phosphor-reflector assembly 116 can include a second interferencereflector disposed on the layer of phosphor material 122 as describedherein, and shown in FIG. 2. Referring to FIG.2,.this second multilayerreflector 26 is shown adjacent the layer of phosphor material 22,however the second multilayer reflector 26 need only be positioned suchthat light can travel between the layer of phosphor material 22 and themultilayer reflector 26, as described above. The second interferencereflector 26 can be a long-pass or short pass reflector. The layer ofphosphor material 22 and the polymeric multilayer reflector 26 can beany desired form such as, for example, planar, shaped or curved.

FIG. 14 is a sectional view of another embodiment of aphosphor-reflector assembly 216 used in the source of FIG. 1. Amultilayer reflector 224 is shown adjacent a layer of phosphor material222, however the multilayer reflector 224 need only be positioned suchthat light can travel between the layer of phosphor material 222 and themultilayer reflector 224. The multilayer reflector 224 is positioned toreflect LED excitation light such as, for example UV, or blue light, andtransmits visible light. This multilayer reflector 224 can be referredto as a long-pass (LP) reflector, as described above.

The multilayer reflector 224 is positioned to reflect LED excitationlight to the layer of phosphor material 222. The multilayer reflector224 can be any useable thickness. The multilayer reflector 224 can be 5to 200 micrometers thick or 10 to 100 micrometers thick. The multilayerreflector 224 can be formed of a material that resists degradation whenexposed to UV light such, as discussed herein. The multilayer reflector224 can optionally be substantially free of inorganic materials.

The multilayer interference reflectors described herein may have alateral thickness gradient, i.e, has a thickness that differs from onepoint on the reflector to another point on the reflector. Thesereflectors may be thicker as the LED emitted light angle of incidenceincreases toward an outer region of the multilayer reflector. Increasingthe reflector thickness at the outer region compensates for a problem ofband shifting, since reflected wavelength is proportional to thicknessand incidence angle.

The multilayer reflector 224 can be positioned in any usableconfiguration with the LED 12 as described herein. In an illustrativeembodiment, the multilayer reflector 224 is positioned between the layerof phosphor 222 and the LED 12. In another illustrative embodiment, thelayer of phosphor 222 is positioned between the multilayer reflector 224and the LED 12. The multilayer reflector 224 can be configured toreflect UV or blue light and transmit at least a portion of the visiblelight spectrum such as green, yellow, or red light. In anotherillustrative embodiment, the multilayer reflector 224 can be configuredto reflect UV, blue or green light and transmit at least a portion ofthe visible light spectrum such as yellow or red light.

The layer of phosphor material 222 is capable of emitting visible lightwhen illuminated with excitation light emitted from an LED 12. The layerof phosphor material 222 can be any useable thickness. The layer ofphosphor material 22 can include any number of binders such as, forexample, a polyester material. In another illustrative embodiment thelayer of phosphor material 222 can include an adhesive material. In afurther illustrative embodiment, an adhesive material can be disposedbetween the layer of phosphor material 222 and the polymeric multilayerreflector 224. The adhesive material can be an optically functionaladhesive.

The phosphor-reflector assembly 216 can be formed in a variety of ways.For example, the layer of phosphor material 222 can be disposed on orcoated on the multilayer reflector 224. The layer of phosphor material222 can be applied as a flowable material on the multilayer reflector224. The layer of phosphor material 222 can be laminated, as a solidlayer, to the multilayer reflector 224. In addition, the layer ofphosphor material 222 and the multilayer reflector 224 can bethermoformed sequentially or simultaneously. The layer of phosphor canbe compressible, elastomeric, and can even be contained in a foamedstructure.

The phosphor-reflector assembly 216 can further include a short-passreflector as described above, and shown in FIG. 2. The layer of phosphormaterial 222 and the multilayer reflector 224 can be any desired formsuch as, for example, planar, shaped or curved.

FIG. 15 is a schematic sectional view of a phosphor based light source310 two-part component system. A phosphor-reflector component 311 can beformed as a unitary component and a LED component 309 can be supplied asa unitary component. The PLED 310 can be formed by positioning the firstoptical component (phosphor-reflector component 311) to receive emittedlight from the second optical component (LED component 309). In anillustrative embodiment, the LED component 309 can have a mating surface308 arranged and configured to mate with the phosphor-reflectorcomponent 311 mating surface 313. The phosphor-reflector 316 isdescribed above. The phosphor-reflector 316 can be disposed within theoptically transparent material 310 or on the optically transparentmaterial surface 320.

EXAMPLES

Measurement of phosphor luminescence herein was made using aspectroradiometer (designated OL 770-LED by Optronic Laboratories, Inc.,Orlando, Fla., USA) fitted with an integrating sphere (designated OLIS-670-LED by Optronic Laboratories) and a high precision LED holder(designated OL 700-80-20 by Optronic Laboratories). Thespectroradiometer is calibrated to report the total radiant energyentering the integrating sphere at the input port (in units of Watts pernanometer). A 1 inch diameter disk was made from the phosphor coatedsample using a custom punch. This disk fits into a custom film adaptormade to mount on the high precision LED holder. The custom adaptor holdsthe film sample approximately one inch above the base of the packagedLED. Measurements were performed by mounting an LED into the holder,placing the film with the phosphor coating into the adaptor, affixingthe adaptor to the light-emitting diode mount and then inserting thediode mount assembly into the entrance aperture of the integratingsphere. If necessary, calibrated neutral density filters were used toadjust the light level reaching the detector of the spectroradiometer.

Unless otherwise stated, the multilayer optical films used in thefollowing examples reflected both polarization states equally at normalincidence (i.e., each of the individual optical layers had nominallyequal refractive indices along orthogonal in-plane axes).

For all of the following examples in which the thickness of the phosphorlayer is given, the thickness was determined by subtracting thethickness of the substrate film from the thickness of the phosphor layerand substrate film together. The thicknesses were measured using a dialindicator (catalog number 52-520-140 by Fred V. Fowler Co., Inc., ofNewton, Mass., USA) with a flat contact point (catalog number52-525-035, also from Fowler) mounted on a dial gage stand (catalognumber 52-580-020, also from Fowler). The thickness of the substratefilm was the average of three measurements at random locations on thesubstrate film. The thickness of the phosphor layer and substrate filmwas the average of six measurements taken at random locations on thephosphor layer.

Example 1

A coating of cerium-doped yttrium aluminum garnet (YAG:Ce) phosphor wasmade on single layer clear poly(ethylene terephthalate) (PET) film bythe following procedure.

12.00 grams of fluorpolymer resin (designated “Phosphor Ink Part A:Resin Solution”, part number: 1INR001, rev: AA, batch number: KY4-035 byDurel Company of Chandler, Ariz., USA) was placed into a 40 milliliterglass jar. 15.02 grams of YAG:Ce phosphor (designated QMK58/F-U1 Lot#13235 by Phosphor Technology, Ltd. of Stevenage, England) was measuredinto a weighing dish. The phosphor was mixed into the resin by firstadding one-half of the phosphor to the resin and mixing it in by handwith a stainless steel spatula and then adding the other half and mixingit by hand. The phosphor and resin were mixed by hand until the mixturehad a smooth texture and uniform appearance. The jar containing theresulting phosphor paste was covered with a lid and placed on a bottleroller for about 30 minutes.

A sheet of single layer clear PET film 3M Company (St. Paul, Minn.) 6inches wide by 10 inches long by 1.5 mils thick was placed on a cleanflat surface. Both surfaces of the PET film were wiped with a lint-freecotton cloth dampened with methanol. The jar containing the phosphorpaste was removed from the bottle roller and about 5 grams of paste wasplaced into a small puddle on the PET film. The phosphor paste washand-drawn into a coating using the 5 mil gap of a square multipleclearance applicator (designated PAR-5357 by BYK-Gardner USA ofColumbia, Md., USA). The wet film was cured at a temperature of about130° C. for 30 minutes in a gravity convection oven (designated Model1350G by VWR International, Inc., of West Chester, Pa., USA). Aftercuring, the phosphor/resin coating thickness was 1.6 mils.

A 1 inch diameter disk of the YAG:Ce coated film was prepared andmounted into the spectroradiometer as described above. The disk wasoriented with the phosphor coated side facing into the integratingsphere. A blue LED (designated Part #25-365 by Hosfelt Electronics,Inc., Steubenville, Ohio) with a peak wavelength of about 463 nm wasused to excite the phosphor. The standard 5 mm package for the blue LEDwas modified by machining off the domed lens at the top of the packageto provide a flat exit face for the blue light. Approximately 0.18 inchof the package was removed from the top of the package. The LED waspowered at 20 milliaamps and 3.46 volts by a constant current powersupply. The emission spectra of the phosphor layer recorded using thespectroradiometer is shown in FIG. 16 as the curve labeled “Example 1”.Using software supplied with the spectroradiometer, the total luminousflux emitted into the integrating sphere was calculated to be 0.068lumens.

Example 2

A piece of multi-layer optical film (MOF) having alternating layers ofPET and co-PMMA and having a normal-incidence reflection band (measuredat half-maximum) from about 600 nm to about 1070 nm (made in accordancewith U.S. Pat. No. 6,531,230) was placed in the film adaptor between thephosphor coated PET film of Example 1 and the blue LED of Example 1(operated at 20 milliamps). The spectrum was recorded and is shown inFIG. 16 as the curve labeled “Example 2”. Using software supplied withthe spectroradiometer, the total luminous flux emitted into theintegrating sphere was calculated to be 0.118 lumens. This represents anincrease in luminous intensity of 73%.

Example 3

A coating of zinc sulfide (ZnS) phosphor was made on poly (ethyleneterepthalate) (PET) film by the following procedure:

20.04 grams of fluorpolymer resin (designated “Phosphor Ink Part A:Resin Solution”, part number: 1INR001, rev: AA, batch number: KY4-035 byDurel Company of Chandler, Ariz., USA) was placed into a 2 ounce glassjar. 20.06 grams of ZnS phosphor (designated GL29A/N-C1 Lot #11382 byPhosphor Technology, Ltd. of Stevenage, England) was measured into aweighing dish. The phosphor was mixed into the resin by first addingone-half of the phosphor to the resin and mixing it in by hand with astainless steel spatula and then adding the other half and mixing it byhand. The phosphor and resin were mixed by hand until the mixture had asmooth texture and uniform appearance. The jar containing the resultingphosphor paste was covered with a lid and placed on a bottle roller forabout 24 hours.

A sheet of clear PET film by 3M Company (St. Paul, Minn.) 6 inches wideby 10 inches long by 1.5 mils thick was placed on a clear flat surface.Both surfaces of the PET film were wiped with a lint-free cotton clothdampened with methanol. The jar containing the phosphor paste wasremoved from the bottle roller and about 3 grams of paste was placedonto the PET film. The phosphor paste was hand-drawn into a coatingusing the 2 mil gap of a square multiple clearance applicator(designated PAR-5353 by BYK-Gardner USA of Columbia, Md., USA). The wetfilm was cured at a temperature of about 130° C. for 30 minutes in agravity convection oven (designated Model 1350G by VWR International,Inc., of West Chester, Pa., USA). After curing the phosphor/resincoating thickness was 0.7 mils.

A one inch diameter disk of the ZnS coated film was prepared and mountedinto the spectroradiometer as described above. The disk was orientedwith the phosphor coated side facing into the integrating sphere. A UVLED (designated Part #25-495 by Hosfelt Electronics, Inc ofSteubenville, Ohio) with a peak wavelength of about 395 nm was used toexcite the phosphor fluorescence. The standard 5 mm package for the UVLED was modified by machining off the domed top of the package toprovide a flat exit face for the UV light. Approximately 0.180 inches ofthe package was removed from the top of the package. The LED was poweredat 20 milliamps and 3.7 volts by a constant current power supply. Theemission spectra of the phosphor layer recorded using thespectroradiometer is shown in FIG. 17 as the curve labeled “Example 3”.Using software supplied with the spectroradiometer, the total luminousflux emitted into the integrating sphere was calculated to be 0.052lumens.

Example 4

A piece of multi-layer optical film (MOF) having alternating layers ofPET and co-PMMA and having a normal-incidence reflection band (measuredat half-maximum) from about 320 nm to about 490 nm (made in accordancewith U.S. Pat. No. 6,531,230) was placed in the film adaptor on top ofthe phosphor layer of Example 3, and the UV LED of Example 3 (operatedat 20 milliamps) was used as the excitation source. The spectrum wasrecorded and is shown in FIG. 17 as the curve labeled “Example 4”. Usingsoftware supplied with the spectroradiometer, the total luminous fluxemitted into the integrating sphere was calculated to be 0.062 lumens.This represents an increase in luminous intensity when compared toExample 3 of about 19%.

Example 5

A broadband visible reflector was made by laminating two pieces ofmulti-layer optical film (MOF). A layer of MOF having alternating layersof PET and co-PMMA and a normal-incidence reflection band (measured athalf-maximum) from about 490 nm to about 610 nm (manufactured by 3MCompany of St. Paul, Minn.) was laminated to a layer of MOF havingalternating layers of PET and co-PMMA and having a normal-incidencereflection band (measured at half-maximum) from about 590 nm to about710 nm (manufactured by 3M Company of St. Paul, Minn.) using a opticallyclear adhesive. The laminate was placed in the film adaptor between thephosphor coated PET film of Example 3, and the UV LED of Example 3(operated at 20 milliamps). A piece of multi-layer optical film (MOF)having alternating layers of PET and co-PMMA and having anormal-incidence reflection band (measured at half-maximum) from about320 nm to about 490 nm (manufactured by 3M Company of St. Paul, Minn.)was placed in the film adaptor on top of the phosphor layer to create acavity having a phosphor layer sandwiched between a visible mirror onthe LED side and a UV/blue mirror on the other side. The spectrum wasrecorded and is shown in FIG. 17 as the curve labeled “Example 5”. Usingsoftware supplied with the spectroradiometer, the total luminous fluxemitted into the integrating sphere was calculated to be 0.106 lumens.This represents an increase in luminous intensity when compared toExample 3 of about 104%.

Example 6

A coating of zinc sulfide (ZnS) phosphor was made on poly (ethyleneterepthalate) (PET) film by the following procedure:

The phosphor paste described in Example 3 was coated onto a sheet ofclear PET film 6 inches wide by 10 inches long by 1.5 mils thick. ThePET was placed on top of a clean flat surface. Both surfaces of the PETfilm were wiped with a lint-free cotton cloth dampened with methanol.About 3 grams of paste was placed onto the PET film. The phosphor pastewas hand-drawn into a coating using the 4 mil gap of a square multipleclearance applicator (designated PAR-5353 by BYK-Gardner USA ofColumbia, Md., USA). The wet film was cured at a temperature of about130° C. for 30 minutes in a gravity convection oven (designated Model1350G by VWR International, Inc., of West Chester, Pa., USA). Aftercuring, the phosphor/resin coating thickness was 1.3 mils.

A one inch diameter disk of the ZnS coated film was prepared and mountedinto the spectroradiometer as described above. The disk was orientedwith the phosphor coated side facing into the integrating sphere. A UVLED (designated Part #25-495 by Hosfelt Electronics, Inc ofSteubenville, Ohio) with a peak wavelength of about 395 nm was used toexcite the phosphor. The standard 5 mm package for the UV LED wasmodified by machining off the domed top of the package to provide a flatexit face for the UV light. Approximately 0.180 inches of the packagewas removed from the top of the package. The LED was powered at 20milliamps and 3.7 volts by a constant current power supply. The emissionspectra of the phosphor layer recorded using the spectroradiometer isshown in FIG. 18 as the curve labeled “Example 6”. Using softwaresupplied with the spectroradiometer, the total luminous flux emittedinto the integrating sphere was calculated to be 0.066 lumens.

Example 7

A piece of multi-layer optical film (MOF) having alternating layers ofPET and co-PMMA and having a normal-incidence reflection band (measuredat half-maximum) from about 490 nm to about 610 nm (manufactured by 3MCompany of St. Paul, Minn.) was placed in the film adaptor between thephosphor coated PET film of Example 6 and the UV LED of Example 6(operated at 20 milliamps). The spectrum was recorded and is shown inFIG. 18 as the curve labeled “Example 7”. Using software supplied withthe spectroradiometer, the total luminous flux emitted into theintegrating sphere was calculated to be 0.095 lumens. This represents anincrease in luminous intensity when compared to Example 6 of about 44%.

Example 8

A coating of zinc sulfide (ZnS) phosphor was made on multi-layer opticalfilm (MOF) by the following procedure:

The phosphor paste described in Example 3 was coated onto a sheet of MOFhaving alternating layers of PET and co-PMMA and having anormal-incidence reflection band (measured at half-maximum) from about490 nm to about 610 nm (manufactured by 3M Company of St. Paul, Minn.).The MOF was placed on top of a clean flat surface. Both surfaces of theMOF film were wiped with a lint-free cotton cloth dampened withmethanol. About 3 grams of paste was placed onto the MOF film. Thephosphor paste was hand-drawn into a coating using the 4 mil gap of asquare multiple clearance applicator (designated PAR-5353 by BYK-GardnerUSA of Columbia, Md., USA). The wet film was cured at a temperature ofabout 130° C. for 30 minutes in a gravity convection oven (designatedModel 1350G by VWR International, Inc., of West Chester, Pa., USA).After curing, the phosphor/resin coating thickness was 1.3 mils.

A one inch diameter disk of the ZnS coated film was prepared and mountedinto the spectroradiometer as described above. The disk was orientedwith the phosphor coated side facing into the integrating sphere. A UVLED (designated Part #25-495 by Hosfelt Electronics, Inc ofSteubenville, Ohio) with a peak wavelength of about 395 nm was used toexcite the phosphor. The standard 5 mm package for the LV LED wasmodified by machining off the domed top of the package to provide a flatexit face for the UV light. Approximately 0.180 inches of the packagewas removed from the top of the package. The LED was powered at 20milliamps and 3.7 volts by a constant current power supply. The emissionspectra of the phosphor layer recorded using the spectroradiometer isshown in FIG. 18 as the curve labeled “Example 8”. Using softwaresupplied with the spectroradiometer, the total luminous flux emittedinto the integrating sphere was calculated to be 0.107 lumens. Thisrepresents an increase in luminous intensity when compared to Example 6of about 62%.

Example 9

A coating of zinc sulfide (ZnS) phosphor was screen printed on thelaminated multi-layer optical film (MOF) described in Example 5 by thefollowing procedure:

150 grams of fluorpolymer resin (designated “Phosphor Ink Part A: ResinSolution”, part number: 1INR001, rev: AA, batch number: KY4-035 by DurelCompany of Chandler, Ariz., USA) was placed into a 16 ounce glass jar.150 grams of ZnS phosphor (designated GL29A/N-C1 Lot #11382 by PhosphorTechnology, Ltd. of Stevenage, England) was measured into a weighingdish. The phosphor was slowly mixed into the resin using a glassimpeller driven by an air motor. The phosphor and resin were mixed untilthe mixture had a smooth texture and uniform appearance. The jarcontaining the resulting phosphor paste was covered with a lid andplaced on a bottle roller for about 10 minutes.

The printing was done using a halftone pattern with a resolution of 28lines per inch on a 280 thread per inch PET screen mounted on a screenprinter (designated Type SSM by Svecia Silkscreen Maskiner AB, ofStockholm, Sweden). The halftone pattern consisted of three regionshaving 10%, 50% and 90% coverage. The pattern was printed in one passonto a sheet of the two laminated MOF films described in Example 5.

The printed layer was cured at a temperature of about 138° C. for 15minutes in a forced air oven. After curing, the phosphor/resin coatingthickness was 0.8 mils.

A one inch diameter disk of the ZnS screen printed film from the portionof the pattern having 50% coverage was prepared and mounted into thespectroradiometer as described above. The disk was oriented with thephosphor coated side facing into the integrating sphere. A UV LED(designated Part #25-495 by Hosfelt Electronics, Inc of Steubenville,Ohio) with a peak wavelength of about 395 nm was used to excite thephosphor. The standard 5 mm package for the UV LED was modified bymachining off the domed top of the package to provide a flat exit facefor the UV light. Approximately 0.180 inches of the package was removedfrom the top of the package. The LED was powered at 20 milliamps and 3.7volts by a constant current power supply. The emission spectra of thephosphor layer recorded using the spectroradiometer is shown in FIG. 19as the curve labeled “Example 9”. Using software supplied with thespectroradiometer, the total luminous flux emitted into the integratingsphere was calculated to be 0.052 lumens.

Example 10

A piece of multi-layer optical film (MOF) having alternating layers ofPET and co-PMMA and having a normal-incidence reflection band (measuredat half-maximum) from about 320 nm to about 490 nm (manufactured by 3MCompany of St. Paul, Minn.) was placed in the film adaptor on top of thephosphor layer of Example 9, and the UV LED of Example 9 (operated at 20milliamps) was used as the excitation source. The spectrum was recordedand is shown in FIG. 19 as the curve labeled “Example 10”. Usingsoftware supplied with the spectroradiometer, the total luminous fluxemitted into the integrating sphere was calculated to be 0.078 lumens.This represents an increase in luminous intensity when compared toExample 9 of about 50%.

Example 11

A thermoformed dome of multilayer optical film (MOF) coated with zincsulfide (ZnS) phosphor was made by the following procedure.

A layer of MOF having alternating layers of PET and co-PMMA and having anormal-incidence reflection band (measured at half-maximum) from about590 nm to about 710 nm (manufactured by 3M Company of St. Paul, Minn.,USA) was bonded to a sheet of poly (vinyl chloride) to form a flexiblecomposite. This composite will be referred to as MOF-PVC.

The MOF-PVC was placed on a clean flat surface with the MOF side facingup. The top surface of the MOF-PVC was wiped with a lint free cottoncloth dampened with methanol. About 3 grams of the ZnS phosphor pastedescribed in Example 9 was placed onto the MOF-PVC. The phosphor pastewas hand-drawn into a coating using the 4 mil gap of a square multipleclearance applicator (designated PAR-5353 by BYK-Gardner USA ofColumbia, Md., USA). The wet film was cured at a temperature of about130° C. for 30 minutes in a gravity convection oven (designated Model1350G by VWR International, Inc., of West Chester, Pa., USA).

The phosphor coated MOF-PVC composite was loaded into a thermoformingmachine. The layer was heated for 23 seconds at a temperature of 270° C.Using a plate with a circular aperture (about ½ inch diameter) thephosphor coated MOF-PVC was formed into a hemisphere of about ½ inchwith the phosphor on the convex side of the hemisphere. Visualinspection of the hemisphere indicated the hemisphere had a greaterthickness near an outer region of the hemisphere and was thinner at aninner region of the hemisphere. The phosphor layer was smooth andcontinuous and exhibited no signs of cracking or delamination.

Example 12

A thermoformed dome of multilayer optical film (NOF) coated with zincsulfide (ZnS) phosphor was made by the following procedure.

A sheet of MOF-PVC described in Example 11 was placed on a clean flatsurface with the MOF side facing up. The top surface of the MOF-PVC waswiped with a lint free cotton cloth dampened with methanol. About 3grams of the ZnS phosphor paste described in Example 9 was placed ontothe MOF-PVC. The phosphor paste was hand-drawn into a coating using the2 mil gap of a square multiple clearance applicator (designated PAR-5353by BYK-Gardner USA of Columbia, Md., USA). The wet film was cured at atemperature of about 130° C. for 30 minutes in a gravity convection oven(designated Model 1350G by VWR International, Inc., of West Chester,Pa., USA).

The phosphor coated MOF-PVC composite was loaded into a thermoformingmachine. The layer was heated for 21 seconds at a temperature of 270° C.Using a plate with a circular aperture (about ½ inch diameter) thephosphor coated MOF-PVC was formed into a hemisphere of about ½ inchwith the phosphor on the convex side of the hemisphere. Visualinspection of the hemisphere indicated the hemisphere had a greaterthickness near an outer region of the hemisphere and was thinner at aninner region of the hemisphere. The phosphor layer was smooth andcontinuous and exhibited no signs of cracking or delamination.

Example 13

A thermoformed dome of multilayer optical film (MOF) coated withcerium-doped yttrium aluminum garnet (YAG:Ce) phosphor was made by thefollowing procedure.

20.01 grams of fluorpolymer resin (designated “Phosphor Ink Part A:Resin Solution”, part number: 1INR001, rev: AA, batch number: KY4-035 byDurel Corporation of Chandler, Ariz., USA) was placed into a 2 ounceglass jar. 19.98 grams of YAG:Ce phosphor (designated QMK58/F-U1 Lot#13235 by Phosphor Technology, Ltd. of Stevenage, England) was measuredinto a weighing dish. The phosphor was mixed into the resin by firstadding one-half of the phosphor to the resin and mixing it in by handwith a stainless steel spatula and then adding the other half and mixingit by hand. The phosphor and resin were mixed by hand until the mixturehad a smooth texture and uniform appearance. The jar containing theresulting phosphor paste was covered with a lid and placed on a bottleroller for about 30 minutes.

A sheet of MOF-PVC described in Example 11 was placed on a clean flatsurface with the MOF side facing up. The top surface of the MOF-PVC waswiped with a lint free cotton cloth dampened with methanol. About 3grams of the YAG:Ce phosphor paste was placed onto the MOF-PVC. Thephosphor paste was hand-drawn into a coating using the 4 mil gap of asquare multiple clearance applicator (designated PAR-5353 by BYK-GardnerUSA of Columbia, Md., USA). The wet film was cured at a temperature ofabout 130° C. for 30 minutes in a gravity convection oven (designatedModel 1350G by VWR International, Inc., of West Chester, Pa., USA).

The phosphor coated MOF-PVC composite was loaded into a thermoformingmachine. The layer was heated for 23 seconds at a temperature of 270° C.Using a plate with a circular aperture (about ½ inch diameter) thephosphor coated MOF-PVC was formed into a hemisphere of about ½ inchwith the phosphor on the convex side of the hemisphere. Visualinspection of the hemisphere indicated the hemisphere had a greaterthickness near an outer region of the hemisphere and was thinner at aninner region of the hemisphere. The phosphor layer was smooth andcontinuous and exhibited no signs of cracking or delamination.

Example 14

A thermoformed dome of multilayer optical film (MOF) coated withcerium-doped yttrium aluminum garnet (YAG:Ce) phosphor was made by thefollowing procedure.

A sheet of MOF-PVC described in Example 11 was placed on a clean flatsurface with the MOF side facing up. The top surface of the MOF-PVC waswiped with a lint free cotton cloth dampened with methanol. About 3grams of the YAG:Ce phosphor paste described in Example 13 was placedonto the MOF-PVC. The phosphor paste was hand-drawn into a coating usingthe 2 mil gap of a square multiple clearance applicator (designatedPAR-5353 by BYK-Gardner USA of Columbia, Md., USA). The wet film wascured at a temperature of about 130° C. for 30 minutes in a gravityconvection oven (designated Model 1350G by VWR International, Inc., ofWest Chester, Pa., USA).

The phosphor coated MOF-PVC composite was loaded into a thermoformingmachine. The layer was heated for 21 seconds at a temperature of 270° C.Using a plate with a circular aperture (about ½ inch diameter) thephosphor coated MOF-PVC was formed into a hemisphere of about ½ inchwith the phosphor on the convex side of the hemisphere. Visualinspection of the hemisphere indicated the hemisphere had a greaterthickness near an outer region of the hemisphere and was thinner at aninner region of the hemisphere. The phosphor layer was smooth andcontinuous and exhibited no signs of cracking or delamination.

Example 15

A sheet of MOF-PVC described in Example 11 was heated in thethermoforming device described above to a temperature of about 270° C.for 16 seconds. This heated sheet of MOF-PVC was draped over thehemispherical lens of a commercially available 5 mm LED package withvacuum assist. The MOF-PVC acquired a final shape corresponding to thehemispherical lens shape.

The formed MOF-PVC transmission spectrum was measured using aPerkin-Elmer Lambda 19 spectrophotometer. The spectrum of the centralportion of the formed MOF-PVC was shown to have band edges at 360 nm and460 nm with a peak reflectivity occurring at 400 nm. This formed MOF-PVFhad a transmission greater than 75% at wavelengths above 500 nm. Thismeasured spectral shift of the MOF-PVC was due to the thinning of theoptical stack occurring during the shaping operation.

All patents and patent applications referenced herein are incorporatedby reference in their entirety. Various modifications and alterations ofthis invention will be apparent to those skilled in the art withoutdeparting from the scope and spirit of this invention, and it should beunderstood that this invention is not limited to the illustrativeembodiments set forth herein.

1. A light source, comprising: an LED that emits excitation light; apolymeric multilayer reflector that reflects the excitation light andtransmits visible light; and a phosphor layer spaced apart from the LED,the phosphor layer comprising particles of phosphor material dispersedin a binder, the phosphor material emitting visible light whenilluminated with the excitation light; wherein the polymeric multilayerreflector reflects excitation light onto the phosphor material layer,and the phosphor layer is disposed between the LED and the polymericmultilayer reflector.
 2. The light source according to claim 1, whereinthe excitation light comprises UV light.
 3. The light source accordingto claim 1, wherein the excitation light comprises blue light.
 4. Thelight source according to claim 1, wherein the binder comprises anadhesive.
 5. The light source according to claim 1, wherein thepolymeric multilayer reflector comprises a polymeric material thatresists degradation when exposed to UV light.
 6. The light sourceaccording to claim 1, wherein the polymeric multilayer reflector issubstantially free of inorganic materials.
 7. The tight source accordingto claim 1, wherein the phosphor layer is discontinuous.
 8. The lightsource according to claim 7, wherein the discontinuous layer comprises apattern of distinct regions.
 9. The light source according to claim 8,wherein the plurality of dots regions each have an area of less than10000 microns².
 10. The light source according to claim 8, wherein theregions comprise a first region that emits red light, a second regionthat emits green light, and a third region that emits blue light, whenilluminated with the excitation light.
 11. The light source according toclaim 1, wherein the polymeric multilayer reflector comprisesalternating layers of a first and second thermoplastic polymer whereinat least some of the layers are birefringent.
 12. The light sourceaccording to claim 8, wherein at least a first region emits light at afirst wavelength and a second region emits light at a second wavelengthdifferent than the first wavelength.